In the transportation industry, the use of tandem trailer rigs has become very important, mainly because of its cost-effectiveness. This is because such an arrangement uses only one driver and one tractor at a time, while the load carrying capacity is twice as great. The main difficulty experienced in the past with the using two trailers in tandem is the method by which they are joined together. If, for instance, one uses a standard bogie, there are two articulations, one of which is under the rear end of the front trailer and one of which is under the front end of the rear trailer. Such a double articulation is dangerous, because it permits several kinds of buckling and similar motions between the two trailers, thus leading to accidents. In my U.S. Pat. Nos. 3,933,374 and 4,030,171, I suggested that a solution to this dangerous problem could be brought about by use of an extension protruding beyond the rear of the front trailer. While this arrangement is generally satisfactory, it has the drawback that the intermediate trailer is almost entirely committed to use in tandem rigs and has very little use for running single. Furthermore, it is difficult to back up to a loading dock even when it is provided with the hinged platform shown in the patent. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.
It is, therefore, an outstanding object of the invention to provide a tandem trailer system in which the connection between the trailers provides a single point of pivot or articulation.
Another object of this invention is the provision of a tandem trailer system in which the connection between the trailers remains permanently with one of the trailers and, therefore, is not subject to pilferage or vandalism, as is true when a bogie is left by itself.
It is another object of the instant invention to provide a tandem trailer system in a special forward trailer, which special trailer can be used by itself.
A still further object of the invention is the provision of a tandem trailer system in which the connection between the trailers remains permanently with the front trailer, which front trailer, nevertheless, can be moved close to a loading dock.
It is a further object of the invention to provide a tandem trailer system which is simple in construction, which is inexpensive to manufacture, and which is capable of a long life of useful service with a minimum of maintenance.
With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by claims appended hereto.